The present invention relates to a communication system, and more particularly, to a software controlled frequency hopping digital communication system.
Although digital communication systems have been available in the prior art for some time, the same have been subject to limitations in cost and complexity primarily due to the requirement for detailed hardware for providing information correlation. In such systems, wherein information is converted into a digital format, transmitted and decoded from the digital format to reconstruct the original information, complex hardware has been necessary to correlate the received digital data, especially in frequency hopping systems. Because of the increased cost and complexity of such hardware correlation techniques, digital systems have not been widely utilized in all areas of communication systems. Particularly in frequency hopping systems, the complexity of the system increases greatly as the speed of transmission and number of frequencies used is increased. Accordingly, there has been a need to develop digital systems which can be constructed at lower cost and with less complexity but are capable of improving the performance and reliability of communication in a variety of environments.
With the advent of computer control and, more importantly, the development of microprocessors for performing many of those functions previously performed with only large main-frame computers, there has been an increasing trend to incorporate microprocessor control in digital communication systems. In such instances, the emphasis on software control becomes more important, thereby resulting in continuing emphasis of performing hardware functions with software instructions. Use of software to achieve such control has the benefit of not only reducing the amount of hardware that may be necessary, but also of allowing the equipment to be modified for a variety of purposes, simply by changing the software routines. It will thus be appreciated that reliable hardware configurations compatible with software control are necessary in the search for more simplified and reliable communication systems.
In frequency hopping systems in particular, there are a plurality of functions that are otherwise unnecessary in fixed-frequency communication systems which take the system configuration even more difficult to implement under software control. In particular, frequency hopping systems require internal time synchronization with other user units in a network having multiple users and must also acquire the necessary information capable of receiving and decoding information from a transmitting system to enable a receiver to hop with the frequencies of that transmitting system. While many of the techniques used to enter such data into a communication system are conventional (e.g., PROM entry of frequency hopping pattern based upon user codes and internal time), there are still various functions which must be achieved to enable efficient software control.
In particular, a receiver must have the ability to efficiently acquire synchronization and tracking of a transmitted signal so that the receiver may frequency hop with a transmitting system. Likewise, a user must generate the appropriate codes and frequency hopping pattern consistent with that which can be understood by other users in transmitting in a frequency hopping mode. This means that the user must be able to receive a synchronization preamble in a conventionally coded data fomat transmitted in a frequency hopping system and thereafter decode that data to maintain synchronization and frequency hop with the transmitter. The system must also buffer continuous data from user input prior to its transmission at one frequency rate and thereafter transmit at a higher frequency rate to accommodate the synchronization and other codes that must be added to any message data generated by the user. All of these requirements result in a highly complex system that must meet a variety of user and system criteria.
Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to provide an improved software controlled communication system specifically for use in frequency hopping systems.